The cardiac glycosides, digitoxin and digoxin have been used in the treatment of cardiac failure for many years. Their metabolism proceeds via stepwise cleavage of digitoxose sugars prior to glucuronidation. The nature and location of the enzyme responsible for that cleavage is still not understood. We propose to study these enzyme(s). Sulfasalazine has recently been shown to decrease the blood and urine levels of digoxin in patients. The investigators that reported the interaction suggested that is inhibited the intestinal absorption of digoxin. We propose to study the effect of sulfasalazine on the disposition and toxicity of digitoxin and digoxin. Spironolactone has been used for almost 20 years as an anti-aldosterone diuretic. It is reported to act as a specific receptor antagonist of aldosterone. We propose to study the effect of spironolactone on the biological disposition of aldosterone.